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4AGZE Turbo – Part 2


4AGZE Turbo – Part 2


Part 2 – Preparing the engine.

There are a number of modifications that need to be made to the 4AGZE in order to adopt a turbocharger in place of the factory-fitted supercharger. Here I will outline what has been done to the engine to prepare it for installation into my AE92 Corolla Seca.

The most obvious change is the fitment of a custom exhaust manifold and the turbo itself, in my case an Hitachi HT18. Removing the old, rusted GZE exhaust manifold was a bit of a challenge with a lot of the bolts fairly well seized in place, but nothing a good soaking in CRC couldn’t fix. As well as the five bolts holding the flange, the manifold has a couple of really tough brackets holding it to the block, almost an overkill! Fitting the new exhaust manifold was, as you would expect, straightforward. A new gasket sourced from Toyota was used.

The other major change that was made to the GZE was the switch to an inlet manifold from a 100kw 4AGE. The problem with the 4AGZE version (in a turbo situation) is that the throttle body is on the inlet side of the supercharger. Perhaps there is a way to adapt the throttle body to the standard inlet, but in my case it was easier just to bolt on a 100kw inlet. The first picture shows the standard manifold (pointing up towards the bonnet).

Removing the inlet manifold required the removal of the fuel rail, to get to the top bolts. This is also a good time to pull out the wiring loom if you don’t intend to use the factory computer. You can see here with the standard manifold removed and laid out beside the 100kw manifold, the bolt pattern is an exact match. Good work Toyota 😉

Bolting on the new inlet manifold is, again, a straightforward procedure. The blow-by hose plugs straight in, the cold-start injector bolts in, the vacuum hose from the plenum to the fuel pressure regulator can be reused, and there are even a few spare holes for vacuum pipes. These came in handy for the boost gauge, blow-off valve & map sensor.

The next step was to test fit the turbo onto the exhaust manifold. If you have a close look at the photo below, you will see a problem. The location of the actuator for the wastegate is very close to the flywheel – not enough clearance to bolt the gearbox on. I’d imagine this is a common problem when fitting a turbo to a FWD car that originated from a RWD (mine came from a Mazda RX7). This was resolved by making up a new bracket for the actuator and mounting it further down the turbo housing, then cutting and re-welding the rod that opens the wastegate. Very important to make sure the wastegate stays in the fully shut position when the rod is welded up, otherwise it will continually bleed exhaust gas pressure and limit boost.

Another issue when using a turbo on a non-turbo engine is oil supply for the turbo. As can be seen in this photo, we used a two-way brass fitting in between the oil-pressure sender and the side of the block, close to the oil filter. Braided high-pressure line and brass fittings were used to run the oil feed to the turbocharger.

An oil return from the turbo was plumbed into the sump, towards the top to avoid oil running back through the pipe.

ere is the engine hanging from the engine stand. You might notice the cam covers have been swapped for standard 1600cc 4AGE covers. Shane now has “SUPERCHARGER” covers on his 4AGE powered Levin, so don’t believe him when he tells you it’s blown 🙂
That’s it for the major modifications needed to prepare for the turbo 4AGZE conversion, I’ll cover what’s left in the third article.

Nothing major purchased since the previous article, so I’ll update this in the final article.

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